Of all the ink colors in this line, black is the smoothest I've used!
It does take some getting used to, but the tricks this pen can do are cool!
Writes variable line widths, no skipping, smooth flowy ink, even when you write
fast. Its not scratchy to me, and I am very picky about scratchiness (Hi-Tec C
0.25 mm, I'm looking at you!).
Writiing in English or Japanese (I can't write in any other languages but I'm
sure it handles just the same) looks very pretty and you can even get a lttle
fancy with your script uusing the Letter Pens, without even trying too hard.

Yes, you can use these refills alone without the pen body, but I suggest you
get at least one pen body to try oout. I pprefer using the pen body not just the
refill alone.
(aand, sorry for the typos, I'mtyping on my phone!)

This is hands-down the smallest tip I've ever had the pleasure to use. It writes
so finely, that I was able to write a poem of 107 words on a 2" post it note,
with margins around the outside and between the paragraphs! I was amazed at the
quality of the writing, with very smooth, dark ink. The pen "refill" itself
handles just fine, but I used it with the Kuretake Zig Letter Pen CocoIro Pen
Body - Light Blue, and it was really very pleasant. Definitely recommend for
fine/small writing!

The tip took a few paragraphs for me to get used to but now I love it. I think
this will be my new favorite pen. The ink is smooth and doesn't bleed through. I
bought this along with the pink body. I really like them both!

I know that some people don't like this refill or the pen in general, but I
truly love it! The ink is very fluid but doesn't clump up, and it is one of my
favorite pens to sketch with in my Moleskine Sketchbook because it does not
bleed through the paper unless you go absolutely crazy in one spot on the page.
It gives you the option to write smooth thin lines as well as larger thick
strokes. Give it a try!

I love this pen. The (Super Fine Brush - black) refill writes smooth and dark.
It has a small and firm barely brush point, that allows for some small variation
of line width with pressure. It also writes easily for quick note taking.

It is true that you can use the refills without the pen body. However I find
the body to be well worth it. The pen bodies are very comfortable to hold even
for long times. The texture is smooth but doesn't slip in my hand. The bit of
the refill that sticks out the end of the pen body looked odd at first and
almost kept me from buying it. Now I love it. It looks fine and makes it easy
to see when ink is getting low. And the bodies look great with vivid color.

The one drawback is I feel like the ink runs out just a little fast. I do use
them a lot though, and am used to reservoir fountain pens that hold much more in
general. I do suggest picking up a few spare refills to keep on hand.